Bicycle transmission device

ABSTRACT

A bicycle transmission device for connected to an freehub body on a rear wheel, which has convex keys arranged radially on the periphery, is provided, including a connecting member, a fastener, and a cogset assembly. The connecting member includes a cylindrical body portion, connection keys protruding from periphery of the body portion, a cut groove passing through the body portion, a first and second connecting seats located on two sides of the cut groove. The inner wall of the body portion has concave grooves corresponding to the convex keys. The fastener is connected to the connecting seats to exert a force making them close. The cogset assembly includes a cogset seat and sprockets. The cogset seat has a first socket hole fitting around the connecting member, and connection grooves corresponding and connected to the connection keys; the sprockets with different chain teeth are connected to the cogset seat.

BACKGROUND OF THE INVENTION 1. Technical Field

The present disclosure relates generally to bicycles, and more particularly to a bicycle transmission device.

2. Description of Related Art

With the popularity of bicycles, bicycle transmission devices have become more diverse in structural design. In common bicycle transmission device as disclosed in the specification and FIG. 10 of U.S. Pat. No. 9,771,127, the connecting member installed on the rear wheel has external screw threads, while the adapter has internal screw threads corresponding to the external threads, so that the adapter can be screwed onto the connecting member; in addition, the sprocket is fixed on the outside of the adapter. Thus, when the chain drives the sprocket to turn, the turning force of the sprocket will be transmitted to the adapter, and then to the connecting member through the screw lock, which drive the rear wheel to rotate.

However, said turning force is transmitted through the matching screw threads between the adapter and the connecting member, therefore, if a user applies an excessive pedaling force instantly (e.g., when out-of-saddle sprinting for climbing a hill), the screw threads could be stripped, which may cause wheel slip, making the user take an infirm step and putting the user at risk.

Moreover, in said U.S. Pat. No. 9,771,127, to prevent the sprocket from being loosed, the outer periphery of the adapter has a flange so that its outer diameter is greater than the inner diameter of the center hole of the sprocket; thus, when the adapter is installed to the sprocket, the outer flange of the adapter abuts against the sprocket for fixing. However, during assembling with the abovementioned structure, the sprocket has to be installed to the adapter first, and the adapter with the sprocket is then installed to the connecting member; afterward, a user has to rotate the sprocket and the adapter at the same time to screw the adapter to the connecting member. Therefore, the assembly process is more complicated and difficult.

Furthermore, to reduce the risk of the aforementioned Patent NO. 9771127, other applicants have applied for U.S. Patent Publication No. 2019/0054765. It's known in the specification and FIG. 6 of said Publication No. 2019/0054765 that a groove is provided around the center hole of the base seat of the big chain, and the sprocket has a screw hole. During assembling, exert two forces on two opposite side of the groove first, so that the big sprocket can be fixed on the connecting member by pressing the base seat; afterward, connect the small sprocket to the base seat on the big sprocket, wherein the small sprocket has a perforation corresponding to the screw hole of the big sprocket. At last, screw the small sprocket to the big sprocket by the small bolt passing through the perforation and locking to the screw hole. Thus, the small bolt abuts against the small sprocket so as to prevent the small sprocket from being loosed.

In this way, with the structure in Patent Publication No. 2019/0054765, when the chain drives the big sprocket or the small sprocket to turn, the turning force is transmitted through the big sprocket or the small sprocket from the base seat of the big sprocket to the connecting member, and further drives the rear wheel to rotate. Therefore, force transmission by the screw threads could be avoided so as to prevent the screw threads from being stripped, which may happen in aforementioned U.S. Pat. No. 9,771,127.

However, the small sprocket is fixed to the big sprocket only through the small bolt in said Patent Publication No. 2019/0054765; in practice, during riding the bicycle, continuous vibration would be generated. Moreover, if a user applies an excessive pedaling force instantly to the small sprocket, the small sprocket would be deformed and a shear force which causes mutual displacement of the big and the small sprockets would be generated, wherein the shear force would also be applied to the small bolt. In such case, after a period of riding or high strength riding, the small bolt could be loosed due to continual vibration or the shear force, which brings security concerns.

BRIEF SUMMARY OF THE INVENTION

In view of the above, the primary objective of the present disclosure is to provide a bicycle transmission device which improves the prior art. The bicycle transmission device of the present disclosure has high security and strength, and is easily detachable and maintainable.

The present disclosure provides a bicycle transmission device to be connected to a freehub body of a bicycle, wherein the freehub body is coaxially connected to a rear wheel of the bicycle; the freehub body has a peripheral part and a plurality of convex keys extending along a radial direction of the peripheral part. The transmission device includes a connecting member and a fastener, wherein the connecting member includes a cylindrical body portion which has a first end and a second end, at least a connection key protruding from an outer periphery of the body portion, a cut groove passing through an inner and outer walls of the body portion and extending from the second end to the first end, and a first connecting seat and a second connecting seat respectively located on two sides of the cut groove. Additionally, the connecting member has a plurality of concave grooves formed on the inner wall of the body portion, which are corresponding to the plurality of convex keys for exerting a force on the first connecting seat and the second connecting seat, which makes the two connecting seats be close to each other.

By the above, the body portion of the connecting member fits on the freehub body to connect the concave grooves with the convex keys of the freehub body. Moreover, the force exerted by the fastener on the first connecting seat and the second connecting seat makes the first connecting seat and the second connecting seats be close to each other, so as to fix the connecting member to the freehub body, and to install the bicycle transmission device on the freehub body.

Based on the above, the connecting member further includes a cogset assembly which includes a cogset seat and at least two sprockets. The cogset seat has a first socket hole provided to fit around the connecting member. The cogset seat further has at least a connection groove which is corresponding to and connected to the at least a connection key. The at least two sprockets have different number of chain teeth respectively, and are coaxially connected to the cogset seat.

Based on the above, the connecting member has an internal thread section on the inner wall at the first end of the body portion; the transmission device further includes an affiliated sprocket and a locking ring, wherein the affiliated sprocket includes a chain teeth portion consisting of a predetermined number of chain teeth, which is provided on an outer periphery in a radial direction of the affiliated sprocket. The affiliated sprocket has a second socket hole on an inner periphery in the radial direction of the affiliated sprocket for fitting around the connecting member. The locking ring includes a main body segment and a flange segment, wherein an outer diameter of the flange segment is greater than an outer diameter of the main body segment. The main body segment has an external thread section thereon, which is corresponding to and connected to the internal thread section, so that the flange segment presses on the affiliated sprocket, and then the affiliated sprocket presses one of the at least two sprockets of the cogset assembly.

Based on the above, the cogset seat includes an accessory mounting seat protruding from the first end close to a periphery of the first socket hole. The accessory mounting seat includes at least an accessory mounting key protruding in a radial direction of the accessory mounting seat. The affiliated sprocket has at least an accessory mounting groove formed on an inner wall of the second socket hole, which is corresponding to and connected to the at least an accessory mounting key.

Based on the above, the first connecting seat has a perforation, while the second connecting seat has a screw hole which is coaxial to the perforation. The fastener is a bolt which passes through the perforation and is connected into the screw hole. Screwing the bolt can exert a force on the first connecting seat and the second connecting seat, which makes the first connecting seat and the second connecting seat be close to each other.

Based on the above, the at least a connection key of the connecting member and the concave grooves are located on the same radial plane.

Based on the above, the connection grooves of the cogset seat, the connection keys of the connecting member, and the concave grooves of the connecting member are located on the same radial plane where the convex keys of the freehub body are located on.

Based on the above, a terminal in an axial direction of the cut groove of the connecting member has a curved opening; a diameter of the curved opening is greater than a width of the cut groove.

Based on the above, the cogset seat further has a receiving groove which is provided to accommodate the first connecting seat, the second connecting seat, and the fastener of the connecting member.

Based on the above, the cogset seat includes a plurality of mounting arms which are radially arranged around the first socket hole. Each of the mounting arms has at least a stage in an axial direction, which correspondingly forms at least two mounting surfaces parallel to the axial direction. The at least two sprockets are connected to the at least two mounting surfaces respectively.

Based on the above, the body portion of the connecting member has a recess which is recessed at the second end and is adjacent to the first connecting seat. The fastener includes a body and a head, wherein the body passes through the perforation and is connected into the screw hole. An outer diameter of the head is greater than an outer diameter of the body; the head presses on the first connecting seat and is located in the recess.

In this way, the force transmission pathway of the abovementioned structures can avoid the risk of stripped screw threads, and the structure is not easy to be loosed, and has high security and high strength. Moreover, said structures of the present disclosure is easy to be detached, assembled, and repaired.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The present disclosure will be best understood by referring to the following detailed description of some illustrative embodiments in conjunction with the accompanying drawings, in which

FIG. 1 is a perspective view of the transmission device of the first preferred embodiment of the present disclosure;

FIG. 2 is a lateral view of FIG. 1;

FIG. 3 is an exploded view of FIG. 1;

FIG. 4 is a perspective view of the freehub body to which the first preferred embodiment is installed;

FIG. 5 is a perspective view of the connecting member and the fastener of the first preferred embodiment;

FIG. 6 is a perspective view of the connecting member of the first preferred embodiment from another aspect;

FIG. 7 is an enlarged view of the circle marked X in FIG. 5;

FIG. 8 is an exploded view of the cogset assembly of the first preferred embodiment;

FIG. 9 is a perspective view of the cogset seat of the first preferred embodiment;

FIG. 10 is a perspective view of the cogset seat of the first preferred embodiment from another aspect;

FIG. 11 is a perspective view of the affiliated sprocket of the first preferred embodiment;

FIG. 12 is a perspective view of the locking ring of the first preferred embodiment;

FIG. 13 is a perspective view of the connecting member of the first preferred embodiment and the freehub body, which haven't been connected yet;

FIG. 14 is a perspective view of the connecting member of the first preferred embodiment and the freehub body, which are connected;

FIG. 15 is a lateral view of FIG. 14;

FIG. 16 is a sectional view along the A-A line in FIG. 15;

FIG. 17 is a sectional view along the B-B line in FIG. 15;

FIG. 18 is a perspective view of the structure in FIG. 14 and the cogset assembly, which haven't been connected yet;

FIG. 19 is a perspective view of the structure in FIG. 14 and the cogset assembly, which are connected;

FIG. 20 is a sectional view along the C-C line in FIG. 19;

FIG. 21 is a rear view of FIG. 19;

FIG. 22 is a perspective view of the structure in FIG. 19, the affiliated sprocket, and the locking ring, which haven't been connected yet;

FIG. 23 is a sectional view along the D-D line in FIG. 2;

FIG. 24 is a sectional view along the E-E line in FIG. 2; and

FIG. 25 is a sectional view along the F-F line in FIG. 2.

DETAILED DESCRIPTION OF THE INVENTION

As shown in FIG. 1 to FIG. 3, a first embodiment of the present disclosure, a bicycle transmission device 1, is provided to be connected to a freehub body 100, wherein the freehub body 100 is used to be coaxially connected to a rear wheel of a bicycle (not shown). The junction of the freehub body 100 and the rear wheel has a joint part 101 which is used as a unidirectional ratchet to be connected to the rear wheel of a bicycle. Furthermore, when the freehub body 100 rotates in a driving direction, it can drive the rear wheel to rotate, while when the freehub body 100 rotates in a non-driving direction which is opposite to the driving direction, it will not drive the rear wheel to rotate; the structure is not described in detail herein because it is not the focus of the present disclosure. In the preferred embodiment of the present disclosure, as shown in FIG. 4, the freehub body 100 has a peripheral part 102 and a plurality of convex keys 103 arranged radially along the peripheral part 102. Additionally, the freehub body 100 includes a base seat 104 which extends in the direction opposite to the joint part 101.

In order to specify the technology of the present disclosure, the structure of each component of the transmission device 1 of the first preferred embodiment is described as follows. As shown in FIG. 1 to FIG. 3, the transmission device 1 includes a connecting member 10, a fastener 20, a cogset assembly 30, an affiliated sprocket 40, and a locking ring 50. As illustrated in FIG. 5 and FIG. 6, the connecting member 10 includes a cylindrical body portion 11 which has a first end 11A and a second end 11B, a plurality of connection keys 12 which protrudes from the outer periphery of the body portion 11; furthermore, the connecting member 10 has a cut groove 13 which passes through the inner and outer walls of the body portion 11, wherein the cut groove 13 extends from the second end 11B to the first end 11A. In addition, as depicted in FIG. 7, the terminal of the cut groove 13 has a curved opening 131, and the diameter R of the opening 131 is greater than the width L of the cut groove 13, so as to form a curved cut groove terminal. Moreover, the connecting member 10 has an internal thread section 14 on the inner wall at the first end 11A of the body portion 11; besides, the connecting member 10 includes a first connecting seat 15 and a second connecting seat 16, which are located at the second end 11B and are respectively provided on two sides of the cut groove 13 in the body portion 11. The first connecting seat 15 has a perforation 151, while the second connecting seat 16 has a screw hole 161 which is disposed corresponding to the perforation 151. Furthermore, the connecting member 10 has a recess 17 which is recessed at the second end 11B and adjacent to the first connecting seat 15. The connecting member 10 has a plurality of concave grooves 18 formed on the inner wall of the body portion 11, which are corresponding to the convex keys 103.

Additionally, for matching the perforation 151 of the first connecting seat 15 and the screw hole 161 of the second connecting seat 16, in this embodiment, the fastener 20 is a bolt having a head 22 and a body 24, wherein the head 22 is located on an end of the body 24, and the outer diameter of the head 22 is greater than the outer diameter of the body 24. The body 24 has screw threads thereon to pass through the perforation 151 and be connected into the screw hole 161. With such design, a user can make the head 22 closely abut against the wall of the first connecting seat 15 around the perforation 151 by turning the fastener 20 so as to exert a force on the first and the second connecting seats 15, 16, which makes said two connecting seats 15, 16 be close to each other. Additionally, the recess 17 is provided to form a free space for the head 22 to move forward to the second connecting seat 16 smoothly during a user is tightening the fastener 20. However, it must be stated that the fastener in the present disclosure is not limited to the bolt. In other embodiments, the fastener can be a C-shaped buckle, a loop, a hook, or other components which can provide a force directly or indirectly to bring the two connecting seats 15, 16 closer.

As shown in FIG. 8, the cogset assembly 30 includes a cogset seat 32 and a plurality of sprockets 34A to 341. Moreover, as illustrated in FIG. 9 and FIG. 10, the cogset seat 32 has a first end 32A and a second end 32B; the cogset seat 32 has a first socket hole 321 in the center thereof, which passes through the first end 32A and the second end 32B; the cogset seat 32 further has a plurality of connection grooves 322 formed on the inner wall of the first socket hole 321 close to the second end 32B, which are located on the same radial plane and corresponding to the aforementioned connection keys; besides, the cogset seat 32 also has a receiving groove 323 corresponding to the position of the first connecting seat 15 and the second connecting seat 16. In this embodiment, the cogset seat 32 includes five radial mounting arms 324 arranged around the first socket hole 321, wherein each of the mounting arms 324 has a plurality of stages from the inside near the first socket hole 321 to the outside away from the first socket hole 321, which correspondingly form a plurality of mounting surfaces 324A to 324H facing the first end 32A; each of the mounting arms 324 has at least a first mounting hole 325 on each of the mounting surfaces 324A to 324H which passes through the mounting arm 324. In addition, the cogset seat 32 includes an accessory mounting seat 326 protruding from the first end 32A close to the periphery of the first socket hole 321, wherein the accessory mounting seat 326 includes a plurality of accessory mounting keys 327 protruding radially.

As shown in FIG. 8, the abovementioned sprockets 34A to 341 have different number of chain teeth respectively, which is corresponding to different diameters of the sprockets. Moreover, the aforementioned sprockets 34A to 341 are arranged from the second end 32B to the first end 32A in descending diameters thereof, and are coaxially mounted on the mounting surfaces 324A to 324I corresponding to the mounting arms 324 of the cogset seat 32. Besides, the sprockets 34A to 34I have a second mounting hole 341 respectively corresponding to the first mounting hole 325 for a rivet (not shown) to pass through so that the sprockets 34A to 34I can be fixed on the mounting surfaces 324A to 324I of the mounting arms, which achieves the purpose of assembling the cogset assembly 30. Of course, in other embodiments, the sprockets can be fixed to the cogset seat by other way instead of rivets; furthermore, the structure for assembly and fixing is not limited to the abovementioned mounting arms.

Additionally, as shown in FIG. 11, in this embodiment, the affiliated sprocket 40 is made in one piece and has three rings of chain teeth portion 41 to 43, wherein each of the chain teeth portions consists of a predetermined number of chain teeth. The number of chain teeth of each ring of chain teeth portion 41 to 43 are different, and the three chain teeth portions 41 to 43 are also sequentially arranged in descending chain teeth thereof. The numbers of the chain teeth of the chain teeth portions 41 to 43 of the affiliated sprocket 40 are all less than the chain teeth of the aforementioned sprockets 34A to 341. Moreover, the affiliated sprocket 40 has a second socket hole 44 in the center, and a plurality of accessory mounting grooves 45 formed on the inner wall of the second socket hole 44, which are corresponding to the shapes of the accessory mounting keys 327. Because the affiliated sprocket 40 is made in one piece, it is not easy to break and the physical strength thereof can be effectively maintained. Of course, the affiliated sprocket in the present disclosure is not limited to be made in one piece; in other embodiment, it can also be an assembled structural design according to other needs (such as reducing the costs of maintenance and replacement).

As shown in FIG. 12, the locking ring 50 has a main body segment 52 and a flange segment 54, wherein the main body segment 52 has an external thread section 521 thereon corresponding to the internal thread section 14. The flange segment 54 is provided at an end of the main body segment 52, and the outer diameter of the flange segment 54 is greater than the outer diameter of the main body segment 52.

The structure of each component of the transmission device 1 of the present disclosure is well described above, while the assembly method with the above structures is specified as follows. When starting to assemble the transmission device 1, a user can fit the body portion 11 of the connecting member 10 around the peripheral part 102 of the freehub body 100 as shown in FIG. 13 in the first place to form an assembly status as shown in FIG. 14 to FIG. 16. In such status, the joint part 101 of the freehub body 100 (i.e., the rear wheel of the bicycle, which is not shown) is closer to the second end 11B of the connecting member 10 than the first end 11A. Moreover, a part of inner wall of the connecting member 10 is in contact with the outer surface of the base seat 104 of the freehub body 100, so that the freehub body 100 can support the connecting member 10. In addition, the convex keys 103 of the freehub body 100 fit in the corresponding concave grooves 18 on the inner wall of the connecting member 10 as illustrated in FIG. 17. Next, the user exerts a force on the first and the second connecting seats 15, 16 to make them closer by tightening the fastener 20, so that the connecting member 10 pinches the freehub body 100 and is fixed to the freehub body 100. Furthermore, through the design of the curved cut groove terminal with the opening 131 which has the diameter R greater than the width L of the cut groove, during the fastener 20 forces the first and the second connecting seats 15, 16 to be closer, the stress applied to the cut groove 13 terminal during the two sides of the cut groove 13 are close to each other will effectively disperses. Thus, the cut groove 13 terminal will not crack due to the stress, which ensures the structural reliability of the transmission device 1. Additionally, through the design of the recess 17 of the connecting member 10 adjacent to the first connecting seat 15, when the fastener 20 screws towards the second connecting seat 16, there is no interference between the head 22 and the connecting member 10, which effectively improves the assembly efficiency and speed of the transmission device 1, and ensures the stability during assembly. In this way, when the connecting member 10 turns, the turning force is transmitted through contact areas where the concave grooves 18 and the convex keys 103 are connected, and thus the connecting member 10 can drive the freehub body 100 to turn synchronously.

After finishing the abovementioned assembly, the cogset assembly 30 can be installed on the connecting member 10 as depicted in FIG. 18. More specifically, the first socket hole 321 of the cogset seat 32 fits around the body portion 11 of the connecting member 10 to form an assembly status as shown in FIG. 19 and FIG. 20, wherein the cogset seat 32 and the sprockets 34A to 341 are coaxially provided on the exterior of the connecting member 10. Moreover, the first end 11A of the connecting member 10, which has the internal thread section 14, will slightly protrude from the cogset seat 32. At the same time, the connection keys 12 of the connecting member 10 are connected to the corresponding connection grooves 322 of the cogset seat 32 as shown in FIG. 21, while the first connecting seat 15, the second connecting seat 16 as well as the fastener 20 of the connecting member 10 are located in the receiving groove 323. In such way, when the cogset assembly 30 turns, the turning force is transmitted through contact areas where the connection grooves 322 and the connection keys 12 are connected, and thus the cogset assembly 30 can drive the connecting member 10 to turn synchronously, and furthermore the connecting member 10 can drive the freehub body 100 to turn as well.

In addition, through the design of the receiving groove 323 accommodating the first connecting seat 15, the second connecting seat 16, and the fastener 20, when the cogset assembly 30 turns, the cogset seat 32 will not be in contact with the fastener 20 which is installed on the first connecting seat 15 and the second connecting seat 16, and therefore avoid the fastener 20 from being loosed due to any physical contact, which improves the reliability and safety of the assembled transmission device 1. Moreover, the first connecting seat 15, the second connecting seat 16, and the fastener 20 can only be located in the receiving groove 323 of the cogset seat 32 rather than the connection grooves 322 of the cogset seat 32, and such structural design limits the cogset assembly 30 to be connected to the connecting member 10 at a predetermined installation angle, which achieves the foolproof effect during assembly, and thus the possibility of incorrectly installing the connecting member 10 during assembly can be significantly reduced. In this way, the assembly speed of the cogset assembly 30 can be increase, and the correctness of assembling the cogset assembly 30 is ensured as well.

After completing the assembly of the connecting member 10 and the cogset assembly 30, the user can assemble the affiliated sprocket 40 and the locking ring 50 in sequence as shown in FIG. 22 to form the structure as illustrated in FIG. 1, FIG. 2, and FIG. 23 so as to finishing the assembly of the transmission device 1. More specifically, during this assembly process, the second socket hole 44 of the affiliated sprocket 40 fits around the accessory mounting seat 326 of the cogset seat 32 first, wherein the accessory mounting keys 327 of the accessory mounting seat 326 are respectively connected to the corresponding accessory mounting grooves 45 of the affiliated sprocket 40 as shown in FIG. 24. Next, pass the main body segment 52 of the locking ring 50 through the second socket hole 44 of the affiliated sprocket 40, and screw the locking ring 50 to connect the external thread section 521 with the internal thread section 14 on the inner wall of the connecting member 10, which makes the main body segment 52 of the locking ring 50 protrude into the connecting member 10. Furthermore, the flange segment 54 of the locking ring 50 presses on the chain teeth portion 43 of the affiliated sprocket 40, and then the affiliated sprocket 40 presses on the sprocket 341 of the cogset assembly 30 so as to firmly press the sprocket 341, and fix the cogset assembly 30 on the connecting member 10, and thus to finish the assembly of the transmission device 1. Additionally, the cogset assembly 30 is connected to the connecting member 10 through the combination of the external thread section 521 of the locking ring 50 and the internal thread section 14 of the connecting member 10, and the threads on the locking ring and the connecting member 10 are bigger and deeper than threads of general bolts, so that the cogset assembly 30 is effectively fixed to the connecting member 10, which prevent them from being loosed due to long-term vibration.

In this way, when the affiliated sprocket 40 turns, the turning force can be transmitted through contact areas where the accessory mounting grooves 45 and the accessory mounting keys 327 are connected, and thus the cogset assembly 40 can drive the cogset seat 32 to turn synchronously. At the same time, the cogset seat 32 drives the connecting member 10 to turn synchronously, which makes the connecting member 10 drive the freehub body 100 to turn synchronously as well.

From the above, with the design of each structure of the transmission device 1, during assembling the transmission device 1, the user only needs to fit the connecting member 10 first, and then screw the fastener 20 firmly, fit the cogset assembly 30, fit the affiliated sprocket 40, and screw the locking ring 50 firmly in sequence, so as to finish the assembly. The assembly process is simple and fast; furthermore, with the abovementioned structures, the force is not transmitted through threads so as to prevent the screw threads from being stripped, which ensures the safety of users when riding.

Moreover, with the structural designs of the connecting member 10 and the cogset seat 32 of the cogset assembly 30 of said transmission device 1, transmission device 1, after assembly, referring to FIG. 25, the convex keys 103 of the freehub body 100 and their corresponding concave grooves 18 of the connecting member 10 as well as the connection keys 12 of the connecting member 10 and their corresponding connection grooves 322 of the cogset seat 32 are all located on the same radial plane. Thus, when the sprockets 34A to 341 are turning, the turning force can be transmitted through the cogset seat 32 more directly to the connecting member 10 and the freehub body 100 in sequence instead of being transmitted through other structures. In this way, the loss of force is substantially reduced during transmission, which ensures the force transmission efficiency of the transmission device 1.

Additionally, with the design of the detachable and replaceable affiliated sprocket 40, users can replace the affiliated sprocket 40 with other affiliated sprocket with different number of rings or chain teeth according to usage requirements, which can meet the needs of customized gear shift. Besides, in other embodiments, the affiliated sprocket 40 can be omitted, while another corresponding locking ring can be provided to press the sprocket 341 or the cogset seat 32 directly, which also achieves the purpose of fixing the cogset assembly 30 to the connecting member 10.

It's known from the above that the force transmission pathway of the transmission device of the present disclosure doesn't do through threads, which avoids the risk of stripped screw threads. Moreover, the structure is not easy to be loosed, and has high security and high strength. Furthermore, the transmission device of the present disclosure is also easy to be detached and assembled, which makes the subsequent maintenance and repair convenient. It must be noted that the embodiments described above are only preferred embodiments of the present disclosure. All equivalent structures which employ the concepts disclosed in this specification and the appended claims should fall within the scope of the present disclosure. 

What is claimed is:
 1. A bicycle transmission device, provided to be connected to a freehub body of a bicycle, wherein the freehub body is coaxially connected to a rear wheel of the bicycle; the freehub body has a peripheral part and a plurality of convex keys extending along a radial direction of the peripheral part; the transmission device comprises: a connecting member comprising a body portion, at least a connection key, a cut groove, a first connecting seat, and a second connecting seat, wherein the body portion is cylindrical and has a first end and a second end; the at least a connection key protrudes from an outer periphery of the body portion; the cut groove passes through an inner wall and an outer wall of the body portion, and extends from the second end to the first end; the first connecting seat and the second connecting seat are respectively located on two sides of the cut groove; additionally, the connecting member has a plurality of concave grooves formed on the inner wall of the body portion, which are corresponding to the plurality of convex keys; and a fastener provided to connect the first connecting seat with the second connecting seat for exerting a force on the first connecting seat and the second connecting seat, which makes the first connecting seat and the second connecting seats be close to each other; by the above, the body portion of the connecting member fits on the freehub body to connect the concave grooves with the convex keys of the freehub body; moreover, the force exerted by the fastener on the first connecting seat and the second connecting seat makes the first connecting seat and the second connecting seats be close to each other, so as to fix the connecting member to the freehub body, and to install the bicycle transmission device on the freehub body.
 2. The bicycle transmission device of claim 1, wherein the connecting member further comprises a cogset assembly which comprises a cogset seat and at least two sprockets; the cogset seat has a first socket hole provided to fit around the connecting member; the cogset seat further has at least a connection groove which is corresponding to and connected to the at least a connection key; the at least two sprockets have different number of chain teeth respectively, and are coaxially connected to the cogset seat.
 3. The bicycle transmission device of claim 2, wherein the connecting member has an internal thread section on the inner wall at the first end of the body portion; the transmission device further comprises an affiliated sprocket and a locking ring, wherein the affiliated sprocket comprises a chain teeth portion consisting of a predetermined number of chain teeth, which is provided on an outer periphery in a radial direction of the affiliated sprocket; the affiliated sprocket has a second socket hole on an inner periphery in the radial direction of the affiliated sprocket for fitting around the connecting member; the locking ring comprises a main body segment and a flange segment, wherein an outer diameter of the flange segment is greater than an outer diameter of the main body segment; the main body segment has an external thread section thereon, which is corresponding to and connected to the internal thread section, so that the flange segment presses on the affiliated sprocket, and then the affiliated sprocket presses one of the at least two sprockets of the cogset assembly.
 4. The bicycle transmission device of claim 3, wherein the cogset seat comprises an accessory mounting seat protruding from the first end close to a periphery of the first socket hole; the accessory mounting seat comprises at least an accessory mounting key protruding in a radial direction of the accessory mounting seat; the affiliated sprocket has at least an accessory mounting groove formed on an inner wall of the second socket hole, which is corresponding to and connected to the at least an accessory mounting key.
 5. The bicycle transmission device of claim 1, wherein the first connecting seat has a perforation, while the second connecting seat has a screw hole which is disposed corresponding to the perforation; the fastener is a bolt which passes through the perforation and is connected into the screw hole; screwing the bolt can exert a force on the first connecting seat and the second connecting seat, which makes the first connecting seat and the second connecting seat be close to each other.
 6. The bicycle transmission device of claim 1, wherein the at least a connection key of the connecting member and the concave grooves are located on the same radial plane.
 7. The bicycle transmission device of claim 1, wherein a terminal in an axial direction of the cut groove of the connecting member has a curved opening; a diameter of the curved opening is greater than a width of the cut groove.
 8. The bicycle transmission device of claim 2, wherein the cogset seat further has a receiving groove which is provided to accommodate the first connecting seat, the second connecting seat, and the fastener of the connecting member.
 9. The bicycle transmission device of claim 2, wherein the cogset seat comprises a plurality of mounting arms which are radially arranged around the first socket hole; each of the mounting arms has at least a stage in an axial direction, which correspondingly forms at least two mounting surfaces parallel to the axial direction; the at least two sprockets are connected to the at least two mounting surfaces respectively.
 10. The bicycle transmission device of claim 5, wherein the body portion of the connecting member has a recess which is recessed at the second end and is adjacent to the first connecting seat; the fastener comprises a body and a head, wherein the body passes through the perforation and is connected into the screw hole; an outer diameter of the head is greater than an outer diameter of the body; the head presses on the first connecting seat and is located in the recess. 